Generally, semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (ICs). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
Optical photolithography involves projecting or transmitting light through a pattern made of optically opaque or translucent areas and optically clear or transparent areas on a mask or reticle onto a layer of photosensitive material deposited over a wafer. For many years in the semiconductor industry, optical lithography techniques such as contact printing, proximity printing, and projection printing have been used to pattern material layers of integrated circuits. Lens projection systems and transmission lithography masks are used for patterning, wherein light is passed through the lithography mask to impinge upon a semiconductor wafer or workpiece.
Although assist features such as serifs are often included in patterns to improve the pattern transfer from a lithography mask to a semiconductor device, in many designs, it is desirable for a pattern on a lithography mask to be transferred having exactly the same image as the pattern on the semiconductor device. However, due to diffraction, reflection, and other effects that can occur in a lithography process, rounding of corners of features patterned on a semiconductor device often occurs, which is referred to as “corner rounding.” Corner rounding may vary in lithography systems, due to the type of photoresist used, the wavelength of light or energy used in the exposure process, and other parameters of the lithography process, for example.
It is desirable to determine the amount of corner rounding of a particular lithography process, in order to assess the required amount of tolerancing and other factors that impact semiconductor device performance and yields, for example. Current methods of measuring corner rounding involve taking a scanning electron microscope (SEM) image or photograph from a top view of a semiconductor device having functioning features formed therein, and manually measuring the amount of corner rounding of the functional features of the semiconductor device on the photograph. For example, a ruler is used to physically measure the corner rounding on the photograph. However, these methods are performed by human operators and they are subjective measurements, thus the measurements are prone to errors and variations. The manual measurements of the corner rounding in the SEM photographs are also time-consuming.
Thus, what are needed in the art are improved methods of measuring corner rounding of lithography processes used in the fabrication of semiconductor devices.